Walls aren't necessarily beauties, and most walls simply don't care. They do a tough job, hence they look tough. But people like to please the eye, and roughness isn't exactly what one is usually looking for. If walls don't look neat and charming, one has to take measures.
Limit #7 Superficiality rules
Tiling the roughness is one possible way to get walls look more friendly. It's not only the slick and shiny surface of the tiles, they're also easy to clean. And there is one more thing: the orderly effect of even distances pleases any eye.